Embodiments relate to a fuel tank valve assembly for a fuel tank, and particularly, although not exclusively, to a fuel tank valve assembly comprising a membrane which allows water to continuously drain through the valve assembly, whilst retaining fuel within the fuel tank.
Fuel tanks, and in particular aircraft fuel tanks, are known to be susceptible to water ingress. For example, aircraft fuel tanks are provided with an opening which ensures that the interior of the fuel tank is at atmospheric pressure. However, water may undesirably enter the fuel tank through this opening. For example, during operation, as the aircraft descends warm humid air may be draw into the fuel tank, and water may condense within the fuel tank which is cold since it has been at high altitude. Once within the tank the water mixes with the fuel and settles at the bottom of the tank.
The presence of water within a fuel tank is the cause a number of potentially serious problems. These may affect not only the fuel tank itself, but also its surrounding systems. From a purely economic standpoint, not only does water contamination reduce the amount of fuel that may be stored within a fuel tank, the water that is carried is deadweight. From a more technical standpoint, water contamination may lead to bio-contamination, which may in turn reduce the effectiveness of a fuel or render it unfit for use altogether. Significantly, since aircraft are exposed to extremely low temperatures at high altitudes, water collected within fuel tank may freeze. This may reduce the effective volume of the tank. Further, if water enters other parts of the fuel delivery system, it may freeze and cause more serious problems.
It is known to use a scavenge pump to remove water from the bottom of a tank. Scavenge pumps are typically in the form of an ejector pump and act to draw fluid (including water) from the lower region of the fuel tank and feed it into the engine fuel inlet.
Aircraft fuel tanks are also typically provided with a drainage valve that is located towards the bottom of the tank. Periodically an operator/engineer will manually open the discharge valve so as to release fluid from the bottom of the fuel tank. Water will initially be discharged from the discharge valve, before fuel starts to be discharged. If the scavenge pump has been working as intended, little water should be released before fuel starts to be discharged. If the scavenge pump has not been working correctly, a significant amount of water may be discharged from the fuel tank. This may indicate to the operator/engineer that the scavenge pump may need to be replaced or fixed.
Whilst this arrangement for removing water from a fuel tank may be satisfactory, it requires a scavenge pump which may be susceptible to failure, and a manual operation is required to operate the discharge valve to discharge any excess water.
It is therefore desirable to provide an improved arrangement from removing water from a fuel tank.